Multiplex signaling system



H. S. OSBORNE.

MULTlPL EX SIGNALINGSYSTEM. APPLICATION FILED JULY 28,1.919.

1 ,429,248, PatentedSept. 19, 1922..

r I IN VEN TOR.

Q ATTORNEY Patented Sept. 19,1922.

HAROLD S. OSBORNE, OF NEW YORK, N. Y., ASSIGNOR TO AMERICAN TELEPHONE AN TELEGRAPH COMPANY, A CORPORATION OF N'EW YORK.

ra'un'rrrnnx srenamnc srsrnm- "Application filed iuly 2B, 1919. serial No. 813,817.

To all whom it may concern:

Be it known that I, HAROLD S. OSBORNE, residing at'New York, in the county of New York and State of New York, have invented a certain Improvements in Multi lex Signaling Systems, of which the fo lowing 1s a specification. I

This invention relates to signaling systems and more particularly to signaling sys- 1c tems in which carrier currents are used for the transmission of signals.

Heretofore it has been proposed to secure multiplex transmission-by superposing signals on high frequency carrier currents of difierent frequencies, all ofwhich are impressed upon a common medium of communication so that each frequency constitutes a separate channel for transmission purposes. In order to secure selectivity, it has been proposed to utilize sharply tuned circuits to separate each frequency intoits proper channel at the terminal stations. It has been found, however, that this method of securing selectivity is unsatisfactory, particularly in the case of multiplex transmission over wire lines where thecarrier fro} quencies are not as high as in the case of wireless transmission, for the reason that the sharply tuned circuit only transmits freely a. relatively narrow band of frequencies and distorts frequencies lying on either side of the critical frequency. This follows from the fact that when a carrier frequency is modulated by signaling currents such as voice currents or telegraph currents, for in stance, a band of high frequencies must be transmitted, extending to either side of the normal carrier frequency to an extent equal to the range of frequencies employed for telephone transmission or tele aph transmission as the case may be. bviously, if such a band of frequencies is impressed upon the sharply tuned circuit, the frequencies lying near the middle of the band will be freely transmitted, while those lying to either side will be considerably attenuated so that a large de ee of distortion results.

This difiiculty' ecomes more noticeable the lower the carrier frequency, as the band of frequencies corresponding to the signaling band extends over a relatively eater portion of the resonance curve when t e frequency rangeof he s gna i g band. becomes a substantial percentage of the carrier fre-- quency employed. In the case of wireless signaling systems employing extremely high frequencies, while the difiiculty is present,

it is not so serious, but as the tendency in.

wireless transmission is constantly toward the utilization of lower frequencies,the distortion due-to sharptuning becomes of considerable importance.

It is proposed to overcome the'difliculties above referred, to by utilizing, instead of sharply tuned circuits for selective purposes, apparatus adapted totransmit withuniform amplitude at band of frequencies of any desired width, while substantially suppressing frequencies lying outside of the band. For this purpose the broad band wave filter shown and described in United States pat- .ents to George A. Campbell, Nos. 1,227,123 and 1,127,114, dated May 22, 1917, is well adapted, although any other form of wave filter having thedesired characteristics may be equally satisfactory.

The invention may now be more fully understood fromthe following detailed description, when read in connection with the accompanying drawing in which: a

Figure 1 is a si-mpli ed diagram illustrating the application of the invention to a carrier system involving wire transmission;

Figs. 2 and 3 constitute diagrams illus-' tratinj'gf the application of the 1nvention to the transmittlng and receiving apparatus of a multiplex wireless system, and Figs. 4 to 8,:inclusive, are diagrams showing several different forms of .wave filter adapted for use in connection with the invention.

Referring to Fig. 1,'L designates an ordi nary wire transmission line adapted for low frequency telephonic transmission and for \tliis purpose terminating in. substation sets X and Y. In order that. the line L may be used formultiplex transmission, branches TL, and TL may be bridged across the line at one station for transmission purposes, and branches RL, and RL, may be bridged across the line at a distant station for receiving purposes. Branches TL, and TL, lead to modulating apparatus M and M adapted to modulate high frequency oscillations sup plied by sources S and S in accordance with signals griginating in telephone or.

. lated into low frequency signali telegraph I transmitterslT and T Themo "known character although the well vacuum tubemodulator has been found to be.

ulating apparatus may be of any well nown the most satisfactory t pe. The receivingbranch es JRL and R 2 cad to detecting apparatus D and D whereby the, high fre-.'

quency modulated oscillations are. transcurrentsand impressed upon the receivers 1 and R The apparatus so far, described corresponds to arrangements well known .in' the prior art and disclosed innumerous United States and foreign patents issued to variou patentees. In such systems of the prior art, however, it was proposed to usevrelativelyv high-carrier frequencies. The signaling hand in this'system was therefor relatively narrow with respect to the carrier fre-,

quency so that timed circuits could be used without undue distortion' When frequencies in i the neighborhood of twenty-five 3 nal range.

' T will conform to these requirements.

While but two sections of thousand cycles or lower are used for carrierpurposes, the signal band 1S so large relative to carrier frequency that tuned cirquencies extending to either side of the carrier frequency assigned tothe channel a distance equal to the range of frequencies" corresponding to the signal range, or

(where it is desired to suppress one side band), the band of frequencies transmit ted may extend to only one side of the car-' rier frequency an amount equal to the sig- .As set forth in said C'ampbell patents, there are five general types of filters which- These five forms are illustrated in Figs. lto 8, in elusive. As shown,- each filter comprises a series of sections, each section including both series and shunt impedance elements. each form of filter are illustrated, it will be understood that as many-sections may be provided as are desired. The form of filter shown in Fig. 4 includes series inductance and-capacity in series with the line, andparallel inductance and capacity in shunt with the line. 5 differs from Fig. 4: in that the inductance element in series with theline 1s omitted. F 1g. 6 dlfiers from Fig. t

. neeaaes omitted while Fig. 8 difiers from Fig. 4 in that the inductance of the'shunt combinationis omitted. I I

It will be a parent from Fig. 1 that if filtei's'TF, an RF, are arranged to trans- -mit the same band of frequencies and if filters'TF and RF areal-ranged to transmit a similar band somewhat remote from the band transmitted by filters 'llF, and RF transmission may take lace-between transmitter T and receiver 1 without inerfering with receiver B In, a similar manner, transmission may take place. between transmitter T and receiver R, without affecting'receiver R 1 lln the case illustrated, it is assumed that the bands of frequencies employed in carrier transmission are relatively high with respect to ordinary telephonic fre uencies so as not to reduce any appreciab eefiect upon the recelvers .of the low frequency telephone sets X and .Y.

The general idea disclosed in Fig. 1 may be applied to wireless transmission as illustrated in Figs. 2 and 3. vReferring to Fig. 2, TA designates a transmitting antenna which is coupled through a transformer 10 to a local circuit 11, having branches TL, and TL each ofwhich includes broad band filters and modulating apparatus similar to that described in connection with Fig. 1. In this case the branches are illustrated as being connected in series instead of in parallel as in the case of F ig.- 1, but it will be understood that the series and parallel arrangements are equivalent.

The corresponding receiving arrangement is shown inFig. 3 in which a receiving antenna RA is coupled through a transformer 12 to a circuit 13 having serially included therein branches RL, and RL, leading through filters RF and RF, respectively, to the detecting and receiving apparatus similar to that described in Fig.

- 1.. The filters shown in Figs. 2 and 3 arein all respects similar to those in Fig. 1, thereby enablin transmission to take place between transmitter T and receiver R, and transmitter T and receiver R, without interference.

While the invention has been illustrated as embodied in a telephone transmission system it is' equally applicable, to multiplex "carrier current telegraph transmission and in the latter connection its importance increases the lower the frequency of the carrier current employed. It will be seen that by means of the arrangements above described, selective transmission without distortion'is possible and it will be understood that the invention may be embodied in many or other organizations widely diflltl ' 6O quentty and. having a width substantially without said band.

3. In a signaling system, a transmitting. station, a receiving station, means'atsaid transmitting-station to modulate each of a mitt fer'ent from those illustrated, without departin from the spirit of the invention as define in the following claims;

What is claimed is: 3 1

1. In a si aling system, means to trans- 'mit a plurality of. carrier frequencies, means to impress low frequency signal variations upon each of sand earner frequencies, said signal variations having a frequency range constituting a substantial percentage of the carrier frequency upon which they are impressed, receiving apparatus for'each carrier frequency and selective means associated with each receiving apparatus to pi'event transmission of undesired frequencles to each 'recelvmg apparatus, sa1d selective means being so proportioned and arrangedas to transmit with equal freedom a band of frequencies in'the neighborhoodof said carrier frequency and having a width-substantially equal to the range of frequencies employed in connection with said low frequency signals.

:2. In a si al'ing system, means to trans mit a plurality of carrier frequencies, means to impress low frequency signal variations upon each of said carrier frequencies, said signal variations havlng a frequency range e constituting a substantial percentage of t carrier frequency upon which they are unpressed, receiving apparatusfor each carrier frequency and selective means associated with eachrecelving apparatus to prevent transmission of undesired frequencies to each receiving apparatus, said selective means comprising a broad band filter adapted totransmit with equal freedom a band of frequencies in the neighborhood of said carrier frequency and having a width substantially equal to the range of frequencies employed in connection with said low frequency signals, and adapted to substantially suppress frequencies lying rec iving station, said selective means being so proportioned and arranged" as to trans. mit with equal, freedoma band 10f frequeni cies in the neighborhood. of said carrier freequal to the range of frequencies employed in connection'with said low frequency 'signals. 4; In a. signaling et-em, a transmitting employs .quency signals transmitted to the .corresponding channel.

a substantial from each mo ulating means to the station, a receiving station, means at said transmittin station to modulate each of a plurality of carrier frequencies in accordance with low frequency signal variations, each of said signal variations having a frequency range. constituting a substantial percentage of the corresponding carrier frequency, selective means at the transmitting station for each of said carrier frequencies to determine the. fre uencies to be trans 'mitted from each mo ulating means to the receiving station, said selective means comprising a broad band filter adapted to transmit with equal freedom a'band of frequencies in the neighborhood of said carrier frequency and having a width substantially equal to the range of frequencies employed in connection with said low frequency signals, and adapted to substantially suppress frequencies lying without said 'band.

5. In a signalingsystent, a transmitting station, a receiving station, a plurality of vtransmitting channels at said transmitting station each adapted to transmit a carriercurrent having a frequency individual to that channel, means assoclated with said. channels to impress low frequency signal variations upon said carrier currents, the sial variations of each channel having a frequency range constituting a substantial percentage of the carrier frequency assi ned to the channel, a plurality of receiving 0 annels at the receiving station corresponding to the channels at the transmitting statlon, receiving. apparatus for each receiving channel, and selective'means associated with each of said] receiving channels, said selective means being. so arranged and proportioned as to transmit with equal free dom a band of frequencies in the neighborhood of the carrier ,frequencyessigned to each channel and having a width substantially e ual to the range of frequencies in connection with the .low fre 6. In a signaling system, a transmitting station, a receiving station, a plurality of transmitting'channels at said transmitting station each adapted to transmit carrier currents having a frequency individual to that channel, .means associated with said ice channels to impress low frequency signalvariationslupon said carrier currents, the

signal variations of each channel having a frequency ,rangeconstituting a substantial percentage of the carrier frequency assigned to. the channel, a plurality of 'receiv'in channels at the receiving station correspon ing to the channels at the transmitting sta- :tion,-receiving apparatus for each receiving channel, .and selective means associated with each of said receiving channels,"saids'elective, means each comprising a broad e. 1? adapted. i-ta est W v 7 channel, and selective means for each transmitting channel to determine the frequency out said band.

equal freedom a band of'frequencies in the neighborhood of the carrier frequency assigned to each channel and "having a width substantially equal to the range of frequenciesemployed 'in connection with the low frequency signals transmitted to the corresponding channel}, and adapted to substantially suppress frequencies lying with 7. In a signaling system, a transmitting station, a receiving station, a plurality of 'transmitting'channels at said transmitting station each adapted to transmit carrier currents having a frequency individual to that channelimeans assoc ated with each of said channels to modulate said carrier currents in accordance with low frequency:

signal variations, the signal variations of --ea/ch channel having a frequency range constituting a substantial percentage of the carrier frequency assigned to the channel, a

plurality of receiving channels at the receivingstation; corresponding to the transmitting'channels at thetransmi'tting station, receiving apparatus foreach receiving to be transmitted from the modulating 'me'ans associated with said channel to the transmitting channels at said transmitting station each adapted to tnans'imit carrier currents having a frequency individual to that channel, means associated with each of said channels to modulate said carrier curwithout sai band.

July 1919,

' inaeaee rents in accordance with low frequency signal variations, the signal variations of each channel havmg' a frequency range constituting a substantial, percentage of the carrier frequency assigned to the channel, a

plurality of'receiving channels at the re ceiving station corresponding to the transmitting channels at the transmitting Station, receiving apparatus for each receiving channel, and selective means for each transmitting channel to, determine the frequency to be transmitted from the modulating means associated with said channel to the receivin station, said selective meansveach comprislng abroad band filter adapted to transmit with equal freedom a band of frequencies in the neighborhood of the carrier .frequency-assi ned to each channel-and having a width su stantially equal to the range of frequencies employed in connection with the low frequency signals transmitted to the cones onding channel, and adapted to substantial suppress frequencies lying 9.111 a hi h frequency signaling system the combination of a plurality of communi:

"eating transmitter and receiver circuits,-

each of said transmitter circuits comprising a source of carrier" oscillations of a frequency different from that suppliedby the. remainder of said. transmitter circuits; each of said transmitter circuits also comprising a source of signal oscillations, means for modulating said carrier oscillations in accordance with said signal oscillations, and a band filter adapted to selectively transmit modulated oscillations from. its respective transmitter circuit to the exclusion of difl'erent frequency oscillations from other of said transmitter circuits. 1

In testimony whereof, I have signed my name tothis specification this 25th day of 'nanonn s. o-seonnn 

